Letter from Howard Walter Florey to J W Trevan Has improved assay method - always assay against a standard - gives details of this - discrepancy between Trevan's results and the Oxford standard - ICI agrees with the Oxford standard - ICI uses dilution method of assay, not ring method - helpful to collaborate to fix standard - has heard no more about collaboration between ICI and Trevan's combine - extraction methods largely mechanised - getting material suitable for local application. 21 May 1942